Accept socket.socket in fcntl functions

[dfarley1]

Sockets have a .fileno() method so they work fine here.

[hauntsaninja]

Might be better to use a protocol?

[dfarley1]

Looks like there's already several _HasFileno protocols and _FileObject/_FileDescriptor types defined (sometimes with conflicting definitions!). Is there anywhere "global" we can consolidate the different definitions?

It looks like asyncore.file_dispatcher and termios also have the same issue, I'll add the protocol there as well.

Edit: Follow-up question: assuming we can centralize the definition should we make all classes with a fileno() method inherit from that protocol? There are a ton of them so reducing duplication would be great. Maybe in io if no where else?

[srittau]

Currently we don't have a central location for protocols like these. But I think we could start adding this one to io and marking it @type_check_only. I don't see the point in deriving concrete classes from protocols, after all protocols were designed to be used ad-hoc.

CC @JelleZijlstra

[JelleZijlstra]

Sounds good. Maybe we could add something like a _types module to typeshed to hold these typing-only types; it could also be used for python/mypy#8240.

[dfarley1]

Where would the _types module live? At the top level stdlib/2and3/_types.pyi?

[JelleZijlstra]

Yes

[dfarley1]

Maybe a dumb question but how do you import across "versions"? Will files under stdlib/3 be able to do from _types import ... if it's under 2and3? I can't seem to find where the pythonpath is setup

[JelleZijlstra]

Yes, that should work. The path logic is hardcoded in type checkers, so mypy knows to look at all of stdlib/2and3/, stdlib/3/, etc. when it is typechecking Python 3 code.

[dfarley1]

Continuing on #3584, I changed branch names on my desktop